A protein that takes part in intracellular signalling pathways by recruiting specific components of the pathway in response to activation of the pathway’s receptor molecule. Thus, a particular pathway may have its own specific adaptor(s), designed for key members of that pathway. In general, adaptors lack enzymatic activity themselves but possess at least two types of binding site: one type to bind to the cytoplasmic region of the activated receptor, and others to bind to specific intracellular molecules in such a way that they become activated, for example, through phosphorylation by tyrosine kinases associated with the receptor. See signal transduction.